Busting the electric car myth

No, electric cars don't suck down the same amount of energy as gas guzzlers do.

Published August 25, 2008 10:40AM (EDT)

Dear Pablo,

I was excited to hear that Chevy plans to debut an electric car in 2010. But then a discussion with a friend got me thinking: If the electricity used to charge up an electric car is created by burning fossil fuels, is it better to stick with a gas-powered car with good fuel economy?

It's true that most electric cars get their electricity from the grid, which, in many states, is made up mostly of electricity from coal-fired power plants. In areas where the power comes mostly from hydro, wind or solar, your electric car would be virtually emissions-free. (Any electric-car owner can achieve this by installing a solar carport at home.)

But we can get at your question in a more precise way. The fact is, you can make an apples-to-apples comparison between an electric- and a petroleum-powered car. An electric car doesn't consume gallons of liquid fuel, so you can't measure its use of energy in miles per gallon. Similarly, conventional cars don't run on electricity, so you can't use miles per kilowatt-hour. So how do you do it?

A few months ago I had the opportunity to visit the R&D facility of Tesla Motors in San Carlos, Calif., and I spoke with people there about this very issue. While their Web site boasts a 256-mpg-equivalent efficiency, they prefer a more geek-friendly metric. I will attempt to translate it into layperson's terms.

By looking at the energy input into the vehicle, be it electricity or liquid fuel, versus the distance traveled with that energy, you can come up with a measure of efficiency. The energy unit of choice is the megajoule (1 kWh is equal to 3.6 MJ and a gallon of gasoline contains 132 MJ), and the distance measure of choice is the kilometer.

With that, there are two components to consider: the efficiency of getting energy to the car (well to tank) and the efficiency of the car itself (tank to wheel). When combined, we get an understanding of the car's well-to-wheel efficiency, which is determined by both the design of the car and its energy source.

According to Tesla, the well-to-tank efficiency of gasoline is 81.7 percent, while the well-to-battery efficiency of natural-gas-generated electricity is 52.5 percent. At first glance, the gasoline looks more efficient, but keep in mind that efficiency is lost in the combustion engine. Because of the fact that the Tesla electric roadster has no internal combustion engine and no conventional transmission, its efficiency is an impressive 2.14 km/MJ. For comparison, the hybrid Prius is 0.68 km/MJ, and a conventional Honda Civic is 0.63 km/MJ. When you combine the well-to-tank efficiency with the vehicle's efficiency, the Tesla has a well-to-wheel efficiency of 1.14 km/MJ, compared with 0.556 km/MJ for the Prius.

So the overall efficiency and emissions from the electric car are about twice as good. Because electricity from coal is about twice as dirty as the natural-gas electricity on which Tesla's numbers are based, the emissions from the electric car will, at worst, be comparable to the Prius'.

Despite this impressive efficiency, the Tesla does have a drawback (besides the fact that I'm 6 feet 3 inches tall and can't get my legs under the steering wheel). While the Tesla would be great for an average American's 30-mile commute, it is not road-trip material. (Not that the average American, by any means, could afford the car's $100,000 price tag.) With a 220-mile range and a 3.5-hour charge time, you wouldn't be able to put on the miles to get you through the boring part (corn row, corn row, corn row) of a cross-country trip in one shot.

One car that promises to solve this problem is indeed Chevy's new electric, the Volt, due out in November 2010. Since the batteries and motors have not been finalized, the overall efficiency is not yet known, but it should be well over 100-mpg equivalent. The Volt will be the opposite of a Prius in that it is an electric car with a backup gasoline generator, rather than a gasoline motor with electric backup. The Volt will function like an electric car and be able to be recharged from the electric grid, but on long road trips it will cycle its gasoline engine to top off the batteries. I am eagerly awaiting the release of the Volt -- and am No. 7,792 on the unofficial waiting list. So, yes, electric and plug-in hybrid cars are a better way to go than gas guzzlers, and remain our best transportation bet in reducing greenhouse gas emissions and dependence on oil.

By Pablo Plastic

Got a question about the environment? Ask Pablo at AskPablo@Salon.com.

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